This invention relates to a process for producing N-aryl-2-lactams, N-alkyl-2-lactams, and N-cycloalkyl-2-lactams by reductive amination of lactones with aryl or alkyl nitro compounds utilizing a metal catalyst, which is optionally supported.
Lactams, and particularly pyrrolidones, are important constituents in many industrial applications, including as solvents in chemical reactions, components in ink and coating formulations, coating strippers in the electronics industry, formulating agents in crop protection products, and as intermediates in the production of pharmaceuticals. For example, N-cyclohexyl-2-pyrrolidone is used as a solvent or intermediate in many industrial applications, including the electronics industry (photo-resist stripping solutions), industrial cleaners, oil/gas well maintenance, and fiber dyeing. N-[2-hydroxyethyl]-2-pyrrolidone is useful in industrial cleaning, printing inks, and gasoline and oil additives. N-octyl-2-pyrrolidone is useful, for example, in the manufacture of agricultural products, as a detergent and dispersant, in industrial and metal cleaners, in printing inks and in fiber dyeing.
Pyrrolidone derivatives are generally prepared on an industrial scale by the catalytic or non-catalytic reaction of gamma butyrolactone with an alkyl amine or ammonia. For example, U.S. Pat. No. 4,824,967 describes a vapor phase process for the production of 2-pyrrolidone using xcex3-butyrolactone and ammonia at a temperature of 230-300xc2x0 C. and a pressure of 0.35 MPa to 2.1 MPa. A magnesium silicate catalyst is used which needs to be separated and regenerated following the reaction, and which may trap considerable amounts of the product. U.S. Pat. No. 5,393,888 describes a liquid-phase process for producing 2-pyrrolidone from xcex3-butyrolactone and ammonia in the absence of a catalyst, but at high temperature and pressure; the reaction is carried out at 200-375xc2x0 C. and 4.8 to 12.4 MPa. In U.S. Pat. No. 6,348,601, methanol is reacted with ammonia in the presence of a catalyst, and the resultant mixture of methyl amines is reacted with xcex3-butyrolactone to form N-methyl-2-pyrrolidone. The reaction temperatures are 300-500xc2x0 C. and the pressures are 0.8 to 3.6 MPa. U.S. Pat. No. 6,248,902 describes a liquid-phase, non-catalytic process for the production of N-methyl-pyrrolidone from xcex3-butyrolactone and monomethylamine.
Aryl compounds have also been used as the amine in reactions with lactones. For example, U.S. Pat. No. 3,775,431 describes the synthesis of N-phenyl-xcex3-methyl-xcex3-butyrolactam from xcex3-methyl-butyrolactone and aniline in a reaction that is carried out at a temperature of 250xc2x0 C. under a nitrogen atmosphere. U.S. Pat. No. 5,538,985 describes the synthesis of 1-(4-chlorophenyl)-2-pyrrolidone from a reaction of p-chloroaniline and xcex3-butyrolactone in the presence of hydrochloric acid; the reaction was carried out for 17 hours at temperatures up to 140xc2x0 C.; the product was recovered in a multi-step process. U.S. Pat. No. 6,350,883 describes a gas-phase process for reacting lactones with amines or ammonia in the presence of aluminosilicate zeolites to produce lactams; the reactions are carried out at 180-400xc2x0 C. and 0 to 1 MPa.
An efficient and low cost process for the production of aryl, alkyl and cycloalkyl lactams would be advantageous. The reactions described above do not use nitro compounds. Disclosed herein is a novel, one-step process for converting lactones to aryl, alkyl and cycloalkyl lactams using nitro compounds in the presence of catalysts.
The present invention relates to a process for preparing N-aryl-2-lactam (III), N-cycloalkyl-2-lactam (IV), or a mixture thereof, which comprises the step of contacting a lactone (I) with an aryl nitro compound (II) in the presence of a catalyst and hydrogen gas; 
wherein:
(i) n=-11;
(ii) R1, R2, R3, R4, R5 and R6 taken independently are hydrogen, hydrocarbyl or substituted hydrocarby), C1 to C18 unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted cycloalkyl, unsubstituted or substituted cycloalkyl containing at least one heteroatom, unsubstituted or substituted aryl, and unsubstituted or substituted heteroaryl;
(iii) R7 is an aromatic group having from 6 to 30 carbons, and R8 is a fully or partially reduced derivative of R7.
(iv) N-aryl-2-lactam (III), N-cycloalkyl-2-lactam (IV), or a mixture thereof, may comprise 100% by weight of the total product formed, or wherein additional products may be produced; and
(v) the catalyst is selected from metals from the group consisting of palladium, ruthenium, rhenium, rhodium, iridium, platinum, nickel, cobalt, copper, iron, osmium; compounds thereof; and combinations thereof.
The present invention also relates to a process for preparing N-alkyl-2-lactam (VI) which comprises the step of contacting a lactone (I) with an alkyl nitro compound (V) in the presence of a catalyst and hydrogen gas; 
wherein:
(i) n=0-11;
(ii) R1, R2, R3, R4, R5 and R6 taken independently are hydrogen, hydrocarbyl or substituted hydrocarbyl, C1 to C18 unsubstituted or substituted alkyl, unsubstituted or substituted alkenyl, unsubstituted or substituted cycloalkyl, unsubstituted or substituted cycloalkyl containing at least one heteroatom, unsubstituted or substituted aryl, and unsubstituted or substituted heteroaryl;
(iii) R9 is an alkyl group having from 1 to 30 carbons, and wherein R9 may be C1-C30 unsubstituted or substituted alkyl, C1-C30 unsubstituted or substituted alkenyl, C1-C30 unsubstituted or substituted alkynyl, C3-C30 unsubstituted or substituted cycloalkyl, or C3-C30 unsubstituted or substituted cycloalkyl containing at least one heteroatom;
(iv) N-alkyl-2-lactam (VI) may comprise 100% by weight of the total product formed, or wherein additional products may be produced; and
(v) the catalyst is selected from metals from the group consisting of palladium, ruthenium, rhenium, rhodium, iridium, platinum, nickel, cobalt, copper, iron, osmium; compounds thereof; and combinations thereof.